Characterization and in vitro probiotic assessment of potential indigenous Bacillus strains isolated from soil rhizosphere

BACKGROUND: Probiotics mainly Bacillus species can be advantageous to the host by promoting its intestinal balance. Attempts were made to isolate and identify Bacillus strains from rhizosphere environment. METHODS: The in vitro probiotic criteria were used for screening and characterizing potential Bacillus probiotics. Morphological, physiological and biochemical characteristics as well as 16S rRNA gene sequence analysis were utilized for identification of the isolates. Seven isolates were chosen based on withstanding to acidic condition (pH 2.5) and various bile salt concentrations (1-4%(w/v)). RESULTS: Isolates found to have the least antimicrobial activity against Listeria monocytogenes PTCC 1163, Staphylococcus aureus ATCC 1912 and Bacillus cereus PTCC 1015; however, no activity against Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 25922 was observed. The Bacillus Isolates showed different variation in auto-aggregation features and adhesion to hydrocarbons ranging from 60% to 90% and 10% to 60%, respectively. Excluding isolate 14 that exhibited resistance to penicillin and ampicillin, all the other Bacillus strains were sensitive to the tested antibiotics. All isolates showed relatively low cytotoxic effect on HepG2 cell line except strains 12 and 14. CONCLUSION: Taking together, among the investigated Bacillus isolates, strains 17 and S10 found to be the most promising candidates to fulfill in vitro probiotic specifications